Q Can you tell me more about blackspot?
A Rose blackspot (Diplocarpon rosae) is extremely common and widespread. The symptoms are dark spots with yellow edges, or more irregular dark blotches, visible on both sides of the leaf. Later, the leaves may turn yellow and fall early. In a bad year this can happen very quickly, and lead to complete defoliation. Repeated or severe attacks can seriously weaken plants, though the disease is rarely fatal.
Caption: Blackspot is a common fungal disease on roses
Q How does blackspot spread?
A The fungus which creates the spots produces spores that can be spread by rain splash and air currents, or by gardeners. It develops most quickly in warm, wet conditions. The spores overwinter mostly on the shoots but some overwinter on fallen leaves, and can survive in soil.
Q How do I control blackspot?
A Pruning in spring will remove many of the overwintering spores and reduce infection. Raking up leaves may help, but as spores are so prevalent it may not be worth the effort. If the disease appears in spring, picking off affected leaves can reduce the spread. Don’t bother, however, if the disease does not occur until late summer. You can treat using Bayer Garden Systhane Fungus Fighter or Scotts Fungus Clear Ultra.
Caption: Picking off affected leaves in spring can reduce the spread of blackspot